Preparation method of high-frequency high-stability carbonyl ferromagnetic powder core

Abstract

The invention discloses a preparation method of a high-frequency and high-stability carbonyl ferromagnetic powder core, and belongs to the field of magnetic functional materials. On the basis of organic and inorganic composite coating, a uniform and high-resistance SiO2 insulating coating layer is formed on the surface of carbonyl iron particles by adopting a simplified insulating coating process, and the process does not need to adopt a silane coupling agent to perform surface modification on carbonyl iron powder so as to control the thickness of the SiO2 coating layer within a reasonable interval; weakening of the magnetic performance of the magnetic powder core caused by introduction of the non-magnetic phase is reduced to the maximum extent; the formed magnetic powder core does not need to be subjected to heat treatment, the onion layered special structure of the carbonyl iron powder particles is prevented from being damaged, the preparation process is simplified, operability is high, and the raw material cost is low. According to the preparation method, the bulk resistivity of the material is greatly improved, the magnetic core loss under the high-frequency condition is reduced, the quality factor, the direct-current anti-saturation characteristic, the magnetic conductivity temperature coefficient and the magnetic conductivity frequency change rate of the carbonyl ferromagnetic powder core are optimized, and the prepared magnetic powder core obtains high stability within the high-frequency range of 1-40 MHz.

Description

Technical Field

[0001] The present invention belongs to the field of magnetic functional materials, and particularly relates to a preparation method of a high-frequency and high-stability carbonyl iron magnetic powder core. Background Art

[0002] With the rapid progress of modern communication technologies, magnetic components are continuously developing towards higher frequencies, smaller sizes, and multi-scenario applications, posing higher requirements for the stability of soft magnetic materials. As an important soft magnetic material, carbonyl iron magnetic powder cores are widely used in high-frequency circuits such as filters, high-frequency transceiver modules, and power synthesis modules. Carbonyl iron magnetic powder cores have advantages such as high quality factor, high anti-saturation characteristics, low magnetic permeability temperature coefficient, and low magnetic permeability frequency change rate (the above several characteristics are the "high stability" described in the present invention), and have a decisive impact on the performance of inductors such as operating frequency band, quality factor Q, anti-interference ability, and temperature stability, and have become an indispensable part of high-frequency inductor components.

[0003] Common metal soft magnetic powder cores, such as FeSiAl magnetic powder cores, NiZn ferrites, etc., although they perform well in some aspects, all have a series of problems such as limited high-frequency applications, large magnetic permeability temperature coefficients, and poor DC bias characteristics, and cannot meet the application requirements of high-frequency and high-stability components. The cut-off frequency of carbonyl iron is several hundred MHz or even up to several GHz, so carbonyl iron magnetic powder cores can be better applied in the frequency range of 1 - 40 MHz (the "high frequency" described in the present invention), and carbonyl iron magnetic powder cores exhibit high stability. Although patents on high-frequency and high-performance carbonyl iron magnetic powder cores have been reported, such as Chinese Invention Patent Application CN202211600945.8 discloses "A preparation method and process of a high-Q carbonyl iron powder magnetic core with a magnetic permeability of 35"; CN202211600470.2 discloses "A preparation method of a carbonyl iron soft magnetic core for high-frequency use in the hundreds of MHz", etc., but in the existing reports, there are no examples to support the high-stability performance of carbonyl iron magnetic powder cores in the frequency range of 1 - 40 MHz.

[0004] In the frequency range of 1 - 40 MHz, the main factor affecting the stability of magnetic powder cores is eddy current loss. Therefore, to meet the requirements of the development of inductive magnetic components towards higher frequencies and higher stability, it is necessary to focus on improving the performance and stability of carbonyl iron magnetic powder cores under high-frequency applications. The method of insulation coating is often used to reduce eddy current loss to improve the above problems. Due to its very fine particle size and special onion-like layered structure, carbonyl iron powder is beneficial to reducing eddy current loss and makes it perform better in high-frequency applications. Insulation coating improves the volume resistivity of carbonyl iron magnetic powder cores, which can not only reduce the eddy current loss between particles, making it obtain better magnetic permeability frequency change rate and temperature coefficient, but also prevent the ultra-fine carbonyl iron powder from oxidizing under various working environmental conditions. Summary of the Invention

[0005] The object of the present invention is to propose a preparation method of a high-frequency and high-stability carbonyl iron magnetic powder core in view of the problem that existing metal soft magnetic powder cores cannot have high stability such as high Q value, magnetic permeability frequency stability, magnetic permeability temperature stability, and DC superposition characteristics during high-frequency applications. The carbonyl iron magnetic powder core prepared by the present invention significantly improves its magnetic permeability stability, quality factor, and DC anti-saturation characteristics in the frequency range of 1 to 40 MHz, meeting the development requirements of high-frequency magnetic components for inductors.

[0006] The core idea of the present invention is: based on organic + inorganic composite coating, using the hydrolysis and condensation reaction of tetraethyl orthosilicate to construct a uniform and high-resistance SiO 2 insulating coating layer on the surface of carbonyl iron particles, improving the bulk resistivity of the carbonyl iron magnetic powder core, effectively suppressing eddy current loss, improving the quality factor of the material under high-frequency conditions, and obtaining excellent magnetic permeability frequency stability; at the same time, improving and simplifying the process of generating SiO 2 by the hydrolysis and condensation reaction of tetraethyl orthosilicate to control the thickness of the SiO 2 coating layer within a reasonable range, minimizing the weakening of the magnetic properties of the magnetic powder core caused by the introduction of non-magnetic phases, and obtaining excellent high-frequency stability.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A preparation method of a high-frequency and high-stability carbonyl iron magnetic powder core, comprising the following steps:

[0009] Step 1. Magnetic powder selection:

[0010] Select carbonyl iron powder particles;

[0011] Step 2. Coating:

[0012] Mix the tetraethyl orthosilicate (TEOS) solution with the iron powder particles selected in Step 1 to achieve inorganic insulation coating on the surface of the particles; after the inorganic insulation coating is completed, mix and stir the coated iron powder particles with phenolic varnish to perform organic insulation coating, obtaining a mixed powder with inorganic-organic coating; 2

[0013] Step 3. Granulation:

[0014] Dry, grind, and screen the mixed powder with inorganic-organic coating obtained in Step 2;

[0015] Step 4. Molding:

[0016] Press the granular material obtained in Step 3 into a green compact;

[0017] Step 5. Curing:

[0018] The green body obtained in step 4 is cured at 120-160° C. for 2-4 hours to obtain a high-frequency and high-stability carbonyl ferromagnetic powder core.

[0019] Furthermore, the particle size D50 of the carbonyl iron powder particles in step 1 is ≤2.5 μm.

[0020] Furthermore, in step 2, the process of inorganic insulation coating is specifically as follows:

[0021] (1) Anhydrous ethanol and deionized water are mixed in a volume ratio of (3-3.5):1, and the selected carbonyl iron powder particles are added while mechanically stirring at a low speed (150-180 rpm), wherein 0.5-0.7 g of carbonyl iron powder particles are added to 1 mL of the mixed solvent to obtain a mixed solution A;

[0022] (2) adding aqueous ammonia to the mixed solution A, adjusting the pH value thereof to 7.8 to 8.2, and continuously stirring the mixture mechanically to obtain a mixed solution B;

[0023] (3) adding tetraethyl orthosilicate (TEOS) to the mixed solution B, increasing the mechanical stirring speed to 240-280 rpm, and reacting for 3-5 hours; wherein the mass of tetraethyl orthosilicate (TEOS) accounts for 10-20 wt% of the mass of the carbonyl iron powder particles;

[0024] (4) After the reaction is completed, the precipitate is allowed to stand, and the precipitate is washed with deionized water and anhydrous ethanol for 3 to 5 times, respectively, and dried in an oven at 60 to 80° C. for 1.5 h to obtain SiO 2 Coated carbonyl iron powder.

[0025] Furthermore, in step 2, the mass of the phenolic varnish accounts for 5-7 wt % of the mass of the coated iron powder particles.

[0026] Furthermore, in step 2, the process of organic insulation coating is: dissolving phenolic varnish in anhydrous ethanol to obtain a mixed solution; then, adding the coated iron powder particles to the mixed solution, stirring thoroughly until the anhydrous ethanol is completely volatilized, to obtain an inorganic-organic coated mixed powder.

[0027] Furthermore, in step 3, the sieve used for screening is 40 to 80 meshes.

[0028] Furthermore, in step 4, the pressing pressure is 700-720 MPa, the release agent used is zinc stearate, and the addition amount of the release agent is 0.2 wt%.

[0029] The high-frequency and high-stability carbonyl iron powder core prepared by the method of the present invention has the following electromagnetic properties: in the frequency range of 1-40 MHz, the rate of change of magnetic permeability with frequency ≤ 16%, the temperature coefficient of magnetic permeability ≤ 60 ppm / °C, the quality factor Q ≥ 260 (@10 MHz), and the DC anti-saturation characteristic ≥ 96% (@300 Oe).

[0030] A preparation method of a high-frequency and high-stability carbonyl iron powder core proposed by the present invention aims at the high-stability performance of the carbonyl iron powder core in the frequency range of 1-40 MHz. By using the hydrolysis reaction of tetraethyl orthosilicate, the surface of the carbonyl iron powder is uniformly coated with SiO 2 , improving the high-frequency stability of the carbonyl iron powder core and broadening the application frequency band of the carbonyl iron powder core to meet its application requirements of high-frequency and high-stability as an inductor component. Since the carbonyl iron powder has relatively high activity, when using tetraethyl orthosilicate hydrolysis for coating, a silane coupling agent is usually introduced to modify the surface of the carbonyl iron powder. However, the introduction of the silane coupling agent may trigger some unnecessary side reactions, thus affecting the structure and performance of the final coating layer. In the present invention, there is no need to introduce a silane coupling agent, which can maximize the preservation of the original properties of the carbonyl iron powder, enabling it to better play its role in subsequent applications and simplifying the insulation coating process. In addition, for the carbonyl iron powder and its powder core, if the heat treatment temperature is too high, the "onion head" structure of the carbonyl iron powder particles will be damaged, deteriorating the high-frequency soft magnetic properties of the material. In the present invention, there is no need to perform heat treatment on the carbonyl iron powder and the powder core, which simplifies the preparation process flow while maintaining excellent properties.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] The present invention provides a preparation method of a high-frequency and high-stability carbonyl iron powder core applicable to the frequency range of 1-40 MHz. Based on organic + inorganic composite coating, a uniform and high-resistance SiO 2 insulation coating layer is formed on the surface of the carbonyl iron particles by using a simplified insulation coating process. This process does not require the use of a silane coupling agent to modify the surface of the carbonyl iron powder to control the thickness of the SiO 2 coating layer within a reasonable range, and to minimize the weakening of the magnetic properties of the powder core caused by the introduction of non-magnetic phases; the formed powder core does not need to be heat-treated, avoiding the destruction of the special onion-layer structure of the carbonyl iron powder particles, simplifying the preparation process, having strong operability, and low raw material cost. This preparation method greatly improves the volume resistivity of the material, reduces the core loss under high-frequency conditions, optimizes the quality factor, DC anti-saturation characteristic, temperature coefficient of magnetic permeability, and rate of change of magnetic permeability with frequency of the carbonyl iron powder core, and the prepared powder core obtains high stability in the 1-40 MHz high-frequency range. Specific embodiments

[0033] In order to meet the demand for high frequency and high stability of magnetic components for inductance, the present invention adopts a simplified insulation coating process to generate SiO by hydrolysis of ethyl orthosilicate. 2 Carbonyl iron powder particles are inorganically coated and the addition ratio of tetraethyl orthosilicate is adjusted to improve the permeability frequency change rate, permeability temperature coefficient, quality factor and DC anti-saturation characteristics of the carbonyl ferromagnetic powder core in the frequency range of 1 to 40 MHz. A high-frequency and high-stability carbonyl ferromagnetic powder core and its preparation method are proposed.

[0034] For ease of understanding, the present invention will be further described below with reference to embodiments.

[0035] Example 1

[0036] Select carbonyl iron powder particles with a particle size D50 ≤ 2.5 μm, weigh 50 g, add it to 800 ml of alcohol aqueous solution (the volume ratio of anhydrous ethanol to deionized water is 3:1), mechanically stir for 5 minutes, drop 40-50 ml of ammonia water to adjust the pH value of the solution to 7.8-8.2, then add 10 wt% of ethyl orthosilicate to react for 3-5 hours, after the reaction is completed, let it stand and precipitate to take out the particles, and wash the obtained particles with deionized water and anhydrous ethanol for several times, and dry them to obtain SiO 2 Coated carbonyl iron powder.

[0037] Weigh 20g of the above-obtained powder and 1g of phenolic varnish, dissolve the phenolic varnish evenly in anhydrous ethanol, add the powder and stir thoroughly until the anhydrous ethanol is completely volatilized, pass the dried granules through a 40-mesh sieve for granulation, evenly mix 0.2wt% of zinc stearate, and press into shape at a pressure of 710MPa, hold the pressure for 10s, and place the resulting green body in an oven at 140°C for curing for 2 to 4h.

[0038] Example 2

[0039] The difference between Example 2 and Example 1 is that 20 wt% of ethyl orthosilicate is added to prepare SiO 2 The remaining steps are the same as those in Example 1.

[0040] Comparative Example 1

[0041] Compared with Example 1, this comparative example does not add tetraethyl orthosilicate to prepare SiO 2 Coating: directly use phenolic varnish to organically coat the carbonyl iron powder, and the remaining steps are the same as those in Example 1.

[0042] The magnetic powder core samples obtained in the above embodiments and comparative examples were subjected to a DC resistance test using a silver paste conductive method. The volume resistance between the upper and lower surfaces of the magnetic powder core was measured using an LCR digital bridge (TH2826) and the volume resistivity was calculated. The results are shown in Table 1.

[0043] The magnetic powder core samples obtained from the above-mentioned examples and comparative examples were wound with 20 turns of enameled wire with a diameter of Φ0.65 mm. The inductance value (Ls) and quality factor Q of the samples were measured by an Agilent E4991B precision impedance analyzer; the magnetic permeability was calculated from the inductance Ls; the temperature coefficient of magnetic permeability was measured by a TH2838 LCR digital bridge and a high and low temperature alternating test chamber in the temperature range of -55 - 125 °C; 30 turns were wound with enameled wire with a diameter of Φ0.65 mm, and the DC superposition performance of the magnetic powder core was tested by a WAYNE KERR precision magnetic analyzer 3260B. The results are shown in Table 2.

[0044] Table 1 Test results of volume resistivity of different examples and comparative examples

[0045] Sample Volume Resistivity (Ω·m) Example 1 <![CDATA[2.07×10 7 > Example 2 <![CDATA[8.24×10 7 > Comparative Example 1 66.43

[0046] As can be seen from the above table, based on the organic + inorganic composite coating, the SiO 2 insulating coating layer constructed on the surface of carbonyl iron particles by the hydrolysis and condensation reaction of tetraethyl orthosilicate significantly improves the volume resistivity of the carbonyl iron magnetic powder core, which helps to suppress eddy current loss and improve the frequency stability and quality factor of the magnetic permeability of the material.

[0047] Table 2 Test results of electromagnetic properties of different examples and comparative examples

[0048]

[0049] As can be seen from the above table, by introducing a simplified insulation coating process and using an appropriate amount of tetraethyl orthosilicate to coat the carbonyl iron powder with SiO 2 coating, the change rate of magnetic permeability and temperature coefficient of the obtained magnetic powder core are both reduced, and the Q value and DC superposition characteristics are significantly improved, which plays a positive role in improving the high-frequency stability of the carbonyl iron magnetic powder core.

[0050] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any technical solution that does not depart from the present invention or any simple modification or equivalent transformation based on the present invention shall be within the protection scope of the present invention.

Claims

1. A method for preparing a high-frequency and high-stability carbonyl iron powder core, characterized in that: The following steps are involved: Step 1. Magnetic Powder Selection: Select carbonyl iron powder particles; Step 2. Wrapping: Mixing tetraethyl orthosilicate with the iron powder particles selected in step 1 to achieve inorganic insulation coating of the particle surface by SiO2; after the inorganic insulation coating is completed, mixing and stirring the coated iron powder particles with phenolic varnish to perform organic insulation coating to obtain an inorganic-organic coated mixed powder; Step 3. Granulation: Drying, grinding and sieving the inorganic-organic coated mixed powder from step 2; Step 4. Molding: Pressing the granules obtained in step 3 into green compacts; Step 5. Curing: The green body obtained in step 4 is cured at 120-160° C. for 2-4 hours to obtain a high-frequency and high-stability carbonyl ferromagnetic powder core.

2. The method for preparing a high-frequency and high-stability carbonyl iron powder core according to claim 1, characterized in that: The particle size D50 of the carbonyl iron powder particles in step 1 is ≤2.5 μm.

3. The method for preparing a high-frequency and high-stability carbonyl iron powder core according to claim 1, characterized in that: In step 2, the process of inorganic insulation coating is: (1) Anhydrous ethanol and deionized water are mixed in a volume ratio of (3-3.5):1, and carbonyl iron powder particles are added while mechanically stirring at a low speed, wherein 0.5-0.7 g of carbonyl iron powder particles are added to 1 mL of the mixed solvent to obtain a mixed solution A; (2) adding aqueous ammonia to the mixed solution A, adjusting the pH value thereof to 7.8 to 8.2, and continuously stirring the mixture mechanically to obtain a mixed solution B; (3) adding ethyl orthosilicate to the mixed solution B, increasing the mechanical stirring speed, and stirring the mixture for 3 to 5 hours; wherein the mass of ethyl orthosilicate accounts for 10 to 20 wt% of the mass of the carbonyl iron powder particles; (4) After the reaction is completed, the mixture is allowed to stand, and the obtained precipitate is washed and dried to obtain SiO2-coated carbonyl iron powder.

4. The method for preparing a high-frequency and high-stability carbonyl iron powder core according to claim 1, characterized in that: In step 2, the process of organic insulation coating is as follows: dissolving phenolic varnish in anhydrous ethanol to obtain a mixed solution; then, adding the inorganic coated iron powder particles to the mixed solution, stirring thoroughly until the anhydrous ethanol is completely volatilized, to obtain an inorganic-organic coated mixed powder.

5. The method for preparing a high-frequency and high-stability carbonyl iron powder core according to claim 4, characterized in that: In step 2, the mass of the phenolic varnish accounts for 5-7 wt % of the mass of the iron powder particles after the inorganic coating.

6. The method for preparing a high-frequency and high-stability carbonyl iron powder core according to claim 1, characterized in that: In step 3, the sieve used for sieving is 40 to 80 meshes.

7. The method for preparing a high-frequency and high-stability carbonyl iron powder core according to claim 1, characterized in that: In step 4, the compression molding pressure is 700-720 MPa, the release agent used is zinc stearate, and the addition amount of the release agent is 0.2 wt %.

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